Potential-Energy Surfaces for Heavy-Ion Collisions

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Abstract
We calculate the nuclear potential energy of deformation for the collision of two heavy nuclei by means of a macroscopic-microscopic method. The nuclear macroscopic energy is calculated in terms of a double volume integral of a Yukawa function, and the microscopic shell and pairing corrections are calculated by use of Strutinsky's method from the single-particle levels of a realistic diffuse-surface single-particle potential. The time evolution of the system after the point of first contact is determined by solving the classical equations of motion for incompressible, irrotational hydrodynamical flow. The effect of nuclear viscosity on the fusion path is to slow down the formation of the neck and to inhibit the excitation of collective shape vibrations. For nuclear systems in which the fission saddle point lies well outside the contact point it is possible to interpret experimental fusion cross sections at relatively low bombarding energies in terms of a one-dimensional interaction barrier, as is customarily done. For heavier nuclear systems and higher bombarding energies, where the larger Coulomb and centrifugal forces tend to deform the fusing nuclei and lead to immediate fission, only those dynamical paths that pass inside the fission saddle point contribute significantly to fusion.